The objective of this project is the discovery of new types of drugs which are clinically useful against cancer. The following topics are of current interest: (1) purine nucleosides as antitumor agents and transition-state inhibitors of purine nucleoside phosphorylase and analogs of Neplanocin A, (2) dinucleotide analogs of NAD as IMPD inhibitors, (3) synthesis of cytidine triphosphate synthetase inhibitors, (4) synthesis of diazepinone nucleosides as antitumor agents, (5) preparation of phosphonate analogs of 2',5'-oligoadenosine trimer core and (6) synthesis of differentiating agents.